Apparatus for starting and operating arc lamps



Oct' 9, 1962 A. HALLAY ET'AL 3,058,033

APPARATUS RoR STARTING AND OPERATING ARc LAMPS 2 Sheets-Sheet 1 Filed Jan. 5, 1961 Oct. 9, 1962 A. HALLAY ET AL 3,058,033

APPARATUS FOR STARTING AND OPERATINGl ARC LAMPS Filed Jan. s, 1961 2 sheets-sheet 2 y pa/WZ @am A Zar/76g.

n 3,353,033 Patented Oct. 9, 1962 3,058,033 APPARATUS FR STARTING AND OPERATNG ARC LAMPS Alexander Hallay and .lack E. Haymaker, Fort Wayne,

Ind., assignors to General Electric Company, a corporation of New York Filed Jan. 3, 1961, Ser. No. 80,216 8 Claims. (Cl. 315-289) This invention relates to apparatus for starting and operating an arc lamp and more particularly to a pulse circuit lfor `starting and operating one or more arc lamps containing an inert rare gas of relatively high atomic weight at a pressure not exceeding atmospheric.

Arc lamps containing inert rare gasses of relatively high atomic weight such as xenon, krypton or argon require a high instantaneous loading in order to produce a continuous output in the visible part of Athe spectrum. The eliciency of such lamps increases as the current pulse through the lamp increases. In order to operate larc lamps at high eciency, it is also necessary that the lamps be supplied with high current pulses of short duration. As an example, two serially connected 600 watt xenon lamps with an approximate operating arc drop of 50 volts for each lamp may be operated eiliciently from a 220 volt, 60 cycle alternating current supply with current pulses having a peak of approximately 100 amperes and a pulse width of 500 microseconds. Under these conditions the lamps deliver 120 pulses of light per second. Such a light source is suitable in many applications, such as printing where photosensitive materials are required to be exposed to an intense source of light.

In order to eiiiciently operate such arc lamps, the circuit must be capable of producing the requisite high current pulses of short duration when energized from a standard commercial power source. Further, it is required that suicient current be supplied to the electrodes of the arc lamp between pulses so that an excessively high voltage will not be required to achieve reignition of the lamp a-t the next pulse. Unless such a current is supplied to the arc lamp during pulses, the lamp will extinguish itself by reason of the rapid deionization which takes place between pulses.

In arc lamp circuit applications, it is particularly desirable that the pulse circuit provide good lamp current regulation. Where the pulse circuit does not inherently have good regulation characteristics, it is necessary to employ voltage stabilizers in order to obtain satisfactory operation. Therefore, it is desirable that the pulse circuit possess good regulation characteristics.

Accordingly, an object of this invention is to providev an improved pulse circuit and apparatus incorporating the aforementioned advantages for generating high current pulses to operate an arc lamp.

A more specific object of the invention is to provide a pulse circuit for starting and operating an arc lamp that has improved current regulating characteristics.

The subject matter which we regard as our invention is set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may be understood by referring to the following description taken in connection with the accompanying drawings in which:

In accordance with the invention, we have provided a pulse circuit for operating one or more arc lamps at a high instantaneous loading from an alternating current supply to produce a radiation source with a broad continuum in the visible spectrum.A A serially connected capacitor and saturable reactor are employed inthe pulse circuit to supply the required current pulses to one or more arc discharge lamps. During each half cycle when the capacitor is charged to a voltage at which the saturable reactor saturates, the capacitor discharges and produces a high current pulse through the lamp. A switching means may be provided in series circuit with the capacitor across the first input leads to cause the capacitor to be initially charged.

In another aspect of the invention, we have found that a starting circuit having a serially connected saturable reactor and capacitor can be utilized eifective'ly to provide a starting current pulse across the saturable reactor and the operating circuit. The starting circuit may be excluded from the operating circuit after the lamp has started. If it is desired to exclude the star-ting circuit from the operating circuit after the arc of the lamp is struck, a switching means may be utilized to energize the starting circuit momentarily in order to provide the additional energy required to ignite the lamp.

An apparatus providing continuous pulse operation of arc lamps utilizing the saturating reactor and a capacitor connected across a lamp is described and claimed in Patent No. 2,938,149e-Wiley, dated May 24, 19360, and assigned to the same assignee as the present application. This invention is concerned with an improvement of the apparatus and circuit disclosed in the aforementioned patent. Although the circuit disclosed and claimed in the aforementioned patent has proven to be eminently satisfactory, it was `found that the operating characteristics of the circuit could be further improved and a circuit employing fewer parts can be employed to start and operate lamps of comparable rating.

FIG. 1 is a schematic circuit diagram of pulse circuits for starting and operating an arc lamp in accordance with the invention;

PIG. 2 is a diagrammatic illustration of the saturable reactor used in the operating circuit of the embodiment of the invention shown in FIG. l;

FIG. 3 is a diagrammatic illustration of the saturable reactor used in the starting circuit of the embodiment of the invention shown in lFIG. l;

FIG. 4 shows another operating circuit for a single arc lamp illustrating another embodiment of the invention;

FIG. 5 illustrates the lamp current, capacitor voltage and lamp voltage current waveforms for the circuits of the invention; and

FIG. 6 illustrates a curve showing a plot of percent variation of the line volts versus percent variation in lamp Watts to demonstrate the regulating characteristics of the circuit of the present invention as compared with a comparable circuit of the prior art.

Referring to FIG. 1 of the drawing, the illustrated circuit is intended to start and operate a pair of xenon arc lamps 1l?, 11 at a high instantaneous loading to provide a radiation source having a broad continuum in the visible light spectrum in addition to the usual spectrum of the xenon gas.

Although the principles underlying the generation of radiation in arc lamps are very complex, measurements of spectral energy distribution for are lamps filled with xenon, krypton and argon show similar energy distribution in the visible region. Xenon filled lamps are preferred since they have the highest luminous output per watt.

The lamps 10, 11 used in the illustrative embodiment of the invention were 600 watt PXA xenon lamps. Essential'ly, the lamps 10, llinclude an elongated tubular quartz envelope 12, 13 provided with activated thermionic self-heating electrodes 14, 15 and 16, 17, respectively. Each of the electrodes may be formed of a tungsten wire helix wound about the inner end of an inlead, as is shown schematically in the drawing. The inleads include foil portions 18, 19 and 20, 21 which are comprised of molybdenum and ar-e pinch-sealed through the end of the quartz envelopes 12 and 13, respectively. The quartz envelopes 12, 13 are filled with an inert rare gas of relatively high atomic weight such as Xenon at a pressure below atmospheric of about 40 millimeters of mercury.

It will be appreciated that as the pressure of the gas filling is increased that more starting voltage is required. For example, at a pressure above 160 millimeters of mercury a starting voltage of more than 3,000 volts was required to provide the instantaneous loading required to produce a continuous output in the visible spectrum.

In the illustrative embodiment of the invention shown in FIG. 1, both an operating circuit and a starting circuit is illustrated therein. The dashed rectangle 22 encloses the principal components of the starting circuit. A pair of input terminal leads 23, 24 are provided for connection to a suitable power supply, such as a 220 volt, 60 cycle source, for which the circuit is designed.

The operatingy circuit includes a pair of output leads 26, 27, a saturable reactor 28 having a core 29, switching means 31 and a main capacitor 32. Conductors 33, 34 are provided to connect switching means 31 in series circuit relationship with the main capacitor 32 across input terminal leads 23, 24. As shown in FIG. 1, the serially connected pair of lamps 10, l11 are connected across output leads 26, `27. Switching means 31 is included in the operating circuit so that during the starting condition it can be momentarily closed for the purpose of placing an initial charge on capacitor 32. It will be understood that switching means 31 and 35 may be com- Vbined provided contacts of switching means 31 are closed before the contacts of switching means 35 are.

The starting circuit, as shown in FIG. l, is connected across the input terminal leads 23, 24 of the operating circuit by the starting circuit input terminal leads 36, 37. It will be appreciated that the leads 36, 37 may be connected directly across the power supply, if desired. The starting circuit includes input terminal leads 36, 37, a starting capacitor 38, a starting saturable reactor 39, a switch 35, and a starting winding 40 which is inductively coupled with the saturable reactor 28 of the operating circuit. Although a separate starting circuit is utilized, as shown in the illustrative embodiment of .the invention, it will `be appreciated that other means may =be used to initially start the lamps 10, -11. Thus, the operating circuit of the present invention may be used without the starting circuit shown in FIG. 1, if the lamps 10, 11 are initially ionized by employing a high frequency voltage source to cause the Xenon gas to ionize.

Referring to FIG. 2, the saturable reactor 28 used in the illustrative embodiment of the invention is shown therein. Reactor 28 includes the magnetic core 29 and winding 41. Winding 41 includes two coils of 148 turns, each being Wound on the legs of the magnetic core 29. U-shaped laminations 42 are butted against -I-shaped laminations 43 to form a diagonal butt joint therewith. Preferably, alternate pairs of the laminations are inverted so that the butt joints are overlapped. A starting winding 40 is inductively coupled with the operating winding 41 so that a voltage spike is induced in the operating winding 41 of the saturable reactor 28 suicient to break the arc in the xenon lamps. As shown in FIG. 1, conductors 27 and 30 connect the winding 41 in series circuit with the lamps 10, f11 and the main capacitor 32 of the operating circuit. The starting winding 40 is connected at one end in circuit with saturable reactor 39 by means of conductor 45 and at the other end to input terminal lead 36.

In the exemplification of the invention the core lam- `inations Wer stacked to a height of 2.36 inches. Each leg of the magnetic core 2K9 had a transverse width of 1.25 inches, defining a coil receiving window 46 which was by 1.25 inches. The laminations were fabricated of grain oriented silicon steel.

It was found that if 1/10 of a mil gap was introduced was reduced to 60 percent of its theoretical value of 160,000. Thus, in order to prevent the capacitor 32 from being prematurely discharged, the laminations of the magnetic core should be stacked to minimize the possibility of gaps occurring in the butt joints.

In FIG. 3 We have illustrated diagrammatically a magnetic core 47 and winding 4S of the starting saturable reactor 39 used in the exemplication of the invention. The magnetic core 47 was constructed of U-shaped laminations 49 butted against I-shaped laminations 50 substantially in the same manner as the magnetic core 29 of saturable reactor 2S shown in FIG. 2.

The laminations of saturable reactor 39 were fabricated of grain oriented silicon steel sheet having a thickness of .014 of an inch and had a width of 3A of an inch to define a coil receiving window approximately .934 of an inch -by 3 inches. The height of the lamination stacks of magnetic core 47 was 2% inches. Winding 48 has two coils which were disposed on the legs of the magnetic core 47 and connected in series circuit with Winding 4f) by conductor 45 and with capacitor 38 by conductor 51.

Since the energy supplled to operate the lamps 10, 11 is provided by discharging the capacitor 32, the particular capacitor used in an application will depend on the lamp requirements. For ytwo 600 watt xenon lamps, an energy of approximately three and one-half watts per second Was required to operate the lamps from a 220 volt, 60 cycle supply. A capacitor having a rating of 56 microfarads at 500 volts A.C. was used as operating capacitor 32. A capacitor rated at 10 microfarads at 250 volts A.C. was suicient to provide the additional energy required to start the lamps `10, `11 and was employed as the starting capacitor 38.

In FIG. 4 we have illustrated a pulse circuit for operating 'a single arc lamp 55. The operating circuit includes a pair of output leads `56, 57, input terminal leads 58, 59, a switch 60, capacitor 61, and a saturable reactor 62 having a magnetic core 63. The input terminals 58, 59 are provided `for connection across an alternating current supply and the output leads 56, 57, for connection across lamp 55. Lamp 55, like the arc lamps d0, 111 of FIG. 1, includes an elongated tubular quartz envelope 65, electrodes 66, 67, and foil portions 68, 69. Conductors 70, '71 connect a switch 60 in circuit with capacitor 61 across input terminal leads 58, 59. Switch 60 is momentarily closed during starting so that an initial charge may be placed on the starting capacitor 61. It will be appreciated that the operating circuit shown in FIG. 4 is substantially similar in opera- .tion to the circuit shown in FIG. 1. The current supplied to the lamp 55 during operation is limited by the total reactanee supplied by the serially connected capacitor 61 and saturable reactor 62. It will be noted therefore that capacitor 61 and saturable reactor 62 provide suicient impedance to limit the lamp circuit during operation and effectively control the current Without need for a separate inductive element such as a choke coil.

In order to start the operation of the pulse circuit shown in FIG. 1, the switch 31 is momentarily closed in order that the operating capacitor 32 may be charged. Switch 35 is then momentarily closed so that the starting capacitor 38 may be charged and discharged. When the voltage across the starting capacitor reaches a value at which the starting saturable reactor 39 is saturated, ca pacitor 38 is thereby discharged and current flows through winding 40 causing a voltage spike to be induced in operating saturable reactor 28. This voltage spike provides the additional energy required to start lamps 10, 11. After lamps 10, 11 are ionized, the starting circuit is ineffective in the operating circuit. During each half cycle of operation, the operating capacitor 32 is charged to a voltage which is sufficient to saturate the operating saturable reactor 28 and is discharged` Thus, two pulses of current per in the butt joint, the effective value of the permeability cycle or 120 pulses per second are provided to produce in lamp 10, 11 a spectrum of radiation which contains in addition to the usual line spectrum of xenon gas, a continum of radiation of substantial intensity whose over-all color resembles natural daylight. It will be appreciated that in arc lamps of this type at lower instantaneous loadings only the characteristic spectrum line of the xenon gas is obtained.

Rapid deionization of the lamps if), 11 does not take place since the serially connected capacitor 32 and saturable reactor 28 in its unsaturated condition permits suicient current to ow to the lamps 10, 11 before the saturable reactor 2S is again saturated to maintain the lamp electrodes 14, 15, 16, 17 in a state of thermionic emission during the interval between pulses. `Further, it was found that if the ratio of the unsaturated reactance of saturable reactor Zit to its saturated reactance reaches 1/ 100 or more, the current lamp current waveform in the circuit used to exemplify the invention will not contain lesser intermittent peaks between the main current pulses. Intermittent peaks caused by a partial discharge of the operating capacitor are undesirable since they do not contribute to the lumen output and represents a loss in energy.

The operating circuit shown in FIG. 4 operates in essentially the same manner as the operating circuit shown in FIG. `l. The lamp S5 must be initially ionized by some means which are not shown in the circuit such as a high frequency source. After the lamp 55 is ionized, the switch 60 may then be momentarily closed to cause the operating `capacitor `61 to charge. When the voltage across the operating capacitor 61 reaches a value whereby the saturable reactor 62 saturates, the capacitor 61 is discharged to provide the required current pulses to produce a high instantaneous loading of the lamp 55.

Although in the illustrative embodiment of the invention we have employed magnetic core structures constructed of stacks of a pluraltiy of flat laminations, a toroidal core made of material having a rectangular hysteresis loop characteristic may be employed.

In FIG. 5 we have illustrated the waveforms of the instantaneous lamp current, the instantaneous voltage across the operating capacitor and the instantaneous voltage across the lamps, which waveforms are identified by the letters A, B, C, respectively. The waveforms A, B, C have a common abscissa, time or t. At time t1, it Will be seen from waveform A that the lamp current has reached a positive peak value and from waveform C that the lamp voltage also is at a peak value. As shown by waveform B, the capacitor 32 has discharged at the t1 and thereafter, capacitor 32 is charged in a generally negative direction. It will be noted that capacitor 32. is initially charged at a high rate and then levels off during the greater portion of the half cycle when the voltage reaches the saturation point of saturable reactor 2S at which time capacitor 32 is again discharged. Thus, at time t2, the instantaneous lamp current land voltage is at a maximum peak -value in a negative direction. Thereafter, capacitor 32 is charged in a generally positive direction until the voltage again reaches the saturation point of the saturable reactor 28, and another cycle commences at t3.

As shown in curve B of FIG. 5, it will be seen that the wave shape of the voltage across the capacitor 32| is substantially square. Since the amplitude factor of squareshaped voltage is less than that of a sine wave, the voltage applied to the capacitor 32 does not have a peaked wave shape as is the case where a shunt capacitor is employed.

In view of the fact that the operating capacitor 32 is connected in series circuit relationship with the saturable reactor 28, the starting current is substantially the same as the operating current since it is limited by the impedance of capacitor 32. As compared with circuits of the prior art employing a starting capacitor in shunt with lamps, the starting current in a comparable prior art circuit is approximately four or five times the normal operating current. Thus, the circuit of the invention has the 6 advantage that it does not impose a heavy load on the power supply during starting.

Referring to FIG. 6, there are shown two curves D, E illustrating the regulating characteristics of the circuit of the present invention as compared with a comparable prior art circuit. `Cur-ve D represents a plot of percent variation of lamp watts when the line voltage across terminals 23, 24 of the circuit shown in FIG. 1 ywas increased from zero to 25 percent above and below the line voltage of 220 volts at which the circuit used to exemplify the invention was designed. `Curve E represents a similar curve for a comparable circuit of the prior art utilizing a capacitor connected in shunt with the arc lamps. Thus, it will be clearly seen from curve D that when line voltage was 25 percent above the line voltage of 220 volts, lamp watts increased approximately 2l percent for the operating circuit of the invention. For a comparable prior art circuit, it will be noted that there is an increase of 40 percent in the power supplied to the lamps corresponding to a 25 percent increase in the -line voltage. The improved regulating characteristics of the circuit makes it possible for many applications to employ the circuit of the invention without need for a voltage stabilizer.

Although in the illustrative embodiments of the invention, the terminal leads 23, 24 of FIG. 1 and terminal leads 5'8, 59 of FIG. 4 Aare provided for connection to an alternating current supply, it will be appreciated that where the circuit is intended to be operated with from an alternating current source at lower voltages, a transformer may be used to step-up the voltages. Thus, it will readily be apparent to those skilled in the art that the circuit of the invention can be readily adapted for use with transformers to step-up or step-down the supply voltage.

From the foregoing description, it should be apparent that the operating and starting circuit in accordance with the invention eliminates the need for a current limiting and charging inductor in the operating and the starting circuits. Further, it will be appreciated that employing a capacitor and saturable reactor connected in series circuit relationship provides a pulse circuit having significantly improved regulating characteristics that cannot be achieved in pulse circuits utilizing a condenser connected in shunt with a lamp or lamps.

While we have described above particular embodiments of the invention, many modifications too may be made as will be apparent to those skilled in the art. It is to be understood, therefore, that we intend by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A pulse circuit for starting and operating from an alternating current supply at least one arc lamp at a high instantaneous loading to provide a radiation source with a broad continuum in the visible spectrum, said circuit comprising a pair of input terminal leads for connection across the 4alternating current supply, a first saturable reactor, a -lirst capacitor, a pair of output leads .for connecting at least one arc lamp in series circuit relationship with said tirst saturable reactor and capacitor, circuit means connecting ysaid -first :satura-ble reactor, said rst capaci-tor, and said output leads across said input terminal leads, a pair of second input terminal leads, a second saturable reactor, a -second capacitor, a winding inductively coupled with -said Ifirst saturable reactor, a starting .switching means, anda second circuit means connecting said Winding, said second saturable reactor, said second capacitor and `starting switching means across said second input terminal leads, said starting switching means causing said second Icapacitor .to be charged and discharged in order to provide a firing pulse across said second saturable reactor to ignite ysaid lamp and said first capacitor and saturable reactor providing sufficient impedance to limit the lamp current during operation.

2. The pulse circuit set forth in claim l wherein a switching means is connected in series circuit with said first capacitor across said rst input terminals to cause said capacitor to be initially charged.

3. A pulse circuit `for starting and operating from an alternating current supply at least one arc lamp at a high instantaneous loading so as to provide a source of radiation with a broad continuum in the visible spectrum, said pulse circuit comprising a pair of terminal leads for connection across an alternating current source, a pair of output leads for connection across said lamp, a first serially connected saturable reactor and capacitor connected in series circuit relationship with one of said terminal leads and one of said output leads, the other of said input leads being connected in circuit with `the other of said output leads, a starting circuit including a second serially connected saturable reactor and capacitor, a winding inductively coupled with said iirst satura-ble reactor, `and a switching means, said second serially connected saturable reactor and capacitor, said winding and said switching means being connected in series circuit relationship across said input terminal leads, said starting circuit providing a high current pulse suicient to st-art said lamp and said iirst serially connected capacitor and reactor providing suicient impedance to limit the lamp current during operation.

4. The pulse circuit as `set forth in claim l wherein a switching means -is connected in series circuit with said rst capacitor across said input terminals to cause said capacitor of said rst serially connected saturable reactor and capacitor to be initially charged.

5. A pulse circuit for starting and operating from an alternating current source a pair of serially connected arc lamps at a high instantaneous loading to provide r-adiation source with a -broad continuum in the visible spectrum, said pulse circuit comprising a pair of input terminal leads `for connection across said alternating current source, a pair of output leads for connection across said serially connected lamps, a first capacitor and saturable reactor connected in series circuit relationship, said rst saturahle reactor and capacitor being connected in circuit with one of said input terminal leads and one of said ouput leads, the other of Said input Iterminal leads -being connected in circuit with the other of said output leads, a trst :switching means, said iirst capacitor and said `first switching means lbeing connected across said input terminal leads and said iirst capacitor to cause said capacitor to-be initially charged when said circuit is energized, a second saturable reactor, a `second capacitor, a winding inductively coupled with said tirst saturable reactor, a second switching means, and circuit means con- 8 necting said second serially connected saturable reactor :and capacitor, said winding and said switching means in series circuit relationship across said input terminal leads.

6. A pulse circuit for operating at least an `arc lamp from an alternating current source at an instantaneous loading suiicient to provide a radiation with a broad continuum in the visible spectrum, said circuit comprising a pair of input terminals `for connection across the alternating current supply, a pair of output leads for connection across said lamp, a serially connected saturable reactor and capacitor, said reactor yand said capacitor being connected in series circuit relationship with one of said output leads and one of said input terminal leads, the other of said input terminal leads being connected in circuit with the other of said output leads and means for providing an initial charge on said capacitor connected in circuit therewith.

7. The pulse circuit set forth in claim 6 wherein said saturable reactor has a magnetic core formed of a stack of U-shaped and I-shaped laminations, the ends of the I-shaped laminations being diagonally butted against the ends of the legs of said U-shaped laminations to form a closed magnetic circuit.

8. A pulse circuit `for operating `from an alternating current supply an arc lamp at a high instantaneous loading to provide a radiation source with a broad continuum in the visible spectrum, said pulse circuit comprising a pair of input terminal leads for connection across the alternating current supply, a saturable reactor, a capacitor, a pair of output leads for connecting at least one arc lamp in series circuit relationship with said saturable reactor and capacitor, circuit means connecting said saturable reactor and said capacitor in series circuit relationship, said circuit means including leads connecting said serially connected saturable reactor and capacitor in circuit with one of said output leads and one of said input terminal leads and connecting the other of said input terminal leads in circuit with the other of said output leads and a switching means connected in series circuit relationship with said capacitor across said input terminals to cause said capacitor to be initially charged when said arc lamp is first started, said capacitor and saturable reactor providing sufficient impedance to limit the lamp current during operation.

Wiley May 24, 196() Schultz Sept. 6, 1960 

